1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to antenna time offset in multiple-input-multiple-output (MIMO) transmission and in coordinated multipoint (CoMP) transmission.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). Examples of multiple-access network formats include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.
A wireless communication network may include a number of base stations or node Bs that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.
A base station may transmit data and control information on the downlink to a UE and/or may receive data and control information on the uplink from the UE. On the downlink, a transmission from the base station may encounter interference due to transmissions from neighbor base stations or from other wireless radio frequency (RF) transmitters. On the uplink, a transmission from the UE may encounter interference from uplink transmissions of other UEs communicating with the neighbor base stations or from other wireless RF transmitters. This interference may degrade performance on both the downlink and uplink.
In MIMO, a time offset may exist between transmit antennas of a single transmission point (e.g., single cell/base station MIMO) which may degrade MIMO performance. In coordinated multipoint (CoMP) transmission, multiple base stations (e.g., multiple transmission points) may participate in simultaneous coherent downlink transmission to a UE. Coherent joint CoMP may require time synchronization between the base stations. However, a time offset may also exist between these base stations which may degrade CoMP performance. Thus, there is a need for reporting and accounting for the time offset between multiple transmit antennas to address these issues.